From: Dave Baker
Subject: Re: Making Taps?
Date: 05 Feb 1999
For rethreading - i.e. cleaning out the crap from an existing hole, just grind
flutes along the thread of an old bolt. I just do it by hand against the edge
of a grinding wheel. You only need the first few threads to be relieved like
For cutting new threads do the same but in a high quality cap head bolt which
will be made of 12.9 or similar and will harden and quench nicely. Turn a taper
lead on it, run a nut up and down a few times to clean the burrs, pop it in an
oxy flame until yellow, drop in a bucket of water - Bob's your uncle (well
before the operation he was anyway)
Saves cutting the threads in a piece of bar stock if it is a thread you can get
a bolt for off the shelf. It won't be half as good as a proper tap but it might
get you out of a fix.
Dave Baker at Puma Race Engines (London - England) - specialist flow
development and engine work. .